This invention relates to aircraft instrumentation and, more particularly, to a visual approach aircraft instrument which provides a head-up display of flight path indicia against a background of the outside world to direct the pilot through a multi-segment landing approach.
Aircraft instruments providing a head-up display to guide the pilot along a preselected approach path to a target are known. Such instruments are shown in Gold U.S. Pat. No. 3,128,623, Bateman U.S. Pat. No. 3,654,806 and Bateman et al U.S. Pat. No. 3,686,626.
Systems or circuits which provide information to the head-up display are also known. Kirschner U.S. Pat. No. 3,816,005 discloses circuits which generate the indicia on the screen. Muller U.S. Pat. No. 3,851,303 describes the circuitry for developing a complemented pitch signal to drive the pitch scale reference indicia and for developing a signal to position the flight path bar. The above-noted copending application discloses a circuit for providing flare indicia to aid the pilot just before touchdown.
The systems and the displays known to the prior art include a one-segment, pilot-selected, approach path followed by a flare maneuver to touchdown. Briefly, the pilot selects an aiming point in the background of the outside world on the screen and operates the aircraft to align a vertically movable indicia bar on the instrument with the aiming point. When aligned, the aircraft will fly toward the aiming point at a preselected descent angle, as -3.degree.. When the aircraft approaches touchdown, the flare indicia are displayed providing aid to the pilot in landing the aircraft.
A single preselected approach path, as for example -3.degree., is often undesirable. For example, the terrain around the airport may prohibit the one-segment approach path or, if the airport is located in a metropolitan area, noise abatement regulations may prohibit the aircraft from flying a single-segment approach path.
Accordingly, the need arises for a system which provides a preselected approach path having a first and a second segment, the angle of the first segment being greater than the angle of the second segment.